The following discussion of the background of the invention is merely provided to aid the reader in understanding the invention and is not admitted to describe or constitute prior art to the present invention.
Clostridium difficile (C difficile) is a gram-positive bacterium that causes 250,000 cases of infection (severe diarrhea, pseudomebranous colitis, colonic rupture, sepsis and death) per year in the USA (1-6) which generates thousands of deaths and costs the health care system over 1 billion dollars per year (2, 6). C difficile infects patients in whom, the use of broad spectrum antibiotics has disrupted the normal gut flora.
The bacterium forms spores that makes it persist in all hospital environments (2). C difficile is not only resistant to the broad spectrum of antibiotics which destroy normal gut flora, but has become resistant to vancomycin and metronidozole which have been used in the past to treat C difficile infections. The infection responds initially to these antibiotics but then relapses and despite initial response upon retreatment, recurs again and again (6). A new virulent strain appears to be resistant to multiple antibiotics (2).
Virulence Factors: The infectivity of C difficile is due to 2 exotoxins which are secreted by C difficile: Toxin A and Toxin B. Toxin A has a molecular weight (MW) of 308,000 kilodaltons (kDa) and 2,710 amino acids (AA). Toxin B has a MW of 279,000 kDa and consists of 2,366 AA (3). There is a third virulence factor: Clostridium difficile transferase (CDT) which is present in hypervirulent strains and consists of two factors: CDTa and CDTb genes (4).
Toxin A is responsible for the first step in the disease process, the binding of Toxin A to its cellular receptors on colonic mucosal cells. This binding results in the death of surface mucosal cells in the colon, leading to increased permeability of the colon leading to the bloody watery diarrhea that is characteristic of the disease (3). Toxin A binds to its receptor through a series of repeating units at its carboxyl terminus (3). The disruption of the surface of the colon caused by Toxin A, then opens the door to entry into mucosal epithelial cells in the colon of Toxin B which is much more devastating to these mucosal cells (3) (see discussion in following sections on Toxin B for mechanism of action). Toxin B carries a glucosyltransferase domain (GTD) which kills cells